Two functionally distinct subsets of IL-17 producing γδ T cells

The gamma delta T cells play an important role in both mice and humans as a source of the cytokine IL-17, which is key for immune resistance to certain pathogens. In mice, most of these IL-17 producers, termed gamma delta T-17 cells, actually comprise two distinct types: those expressing an invariant V gamma 6V delta 1(+)TCR and those expressing a V gamma 4(+)TCR. Murine gamma delta T-17 cells acquire an inherent bias to produce IL-17 and other type 17 cytokines during thymic development. The similarities and differences between the two mouse gamma delta T-17 types are reviewed here, and the potential implications of their differences are discussed. There is some evidence that two distinct TCR-defined IL-17-producing gamma delta T cell subsets also exist in humans, but unlike the mouse gamma delta T-17 cells, these cells are probably not imprinted with an IL-17 bias during thymic development, but rather acquire an IL-17 bias in the periphery.